Role of glucose in the regulation of glutamine metabolism in health and in type 1 insulin-dependent diabetes

To determine the effect of glucose availability on glutamine metabolism, glutamine kinetics were assessed under conditions of hyperglycemia resulting from 1) intravenous infusion of 7.5% dextrose in healthy adults and 2) insulin deficiency in young adults with insulin-dependent diabetes mellitus (IDDM). Eight healthy adults and five young adults with IDDM were studied in the postabsorptive state by use of a primed continuous infusion of D-[U-(14)C]glucose, L-[5,5,5-(2)H(3)]leucine, and L-[3, 4-(13)C]glutamine. Whether resulting from insulin deficiency or dextrose infusion, the rise in plasma glucose was associated with increased glucose turnover (23.5 +/- 0.7 vs. 12.9 +/- 0.3 micromol. kg(-1). min(-1), P < 0.01 and 20.9 +/- 2.5 vs. 12.8 +/- 0.4 micromol. kg(-1). min(-1), P = 0.03, in health and IDDM, respectively). In both cases, high blood glucose failed to alter glutamine appearance rate (R(a)) into plasma [298 +/- 9 vs. 312 +/- 14 micromol. kg(-1). h(-1), not significant (NS) and 309 +/- 23 vs 296 +/- 26 micromol. kg(-1). h(-1), NS, in health and IDDM, respectively] and the estimated fraction of glutamine R(a) arising from de novo synthesis (210 +/- 7 vs. 217 +/- 10 micromol. kg(-1). h(-1), NS and 210 +/- 16 vs. 207 +/- 21 micromol. kg(-1). h(-1), NS, in health and IDDM, respectively). When compared with the euglycemic day, the apparent contribution of glucose to glutamine carbon skeleton increased when high plasma glucose resulted from intravenous dextrose infusion in healthy volunteers (10 +/- 0.8 vs. 4.8 +/- 0.3%, P < 0.01) but failed to do so when hyperglycemia resulted from insulin deficiency in IDDM. We conclude that 1) the contribution of glucose to the estimated rate of glutamine de novo synthesis does not increase when elevation of plasma glucose results from insulin deficiency, and 2) the transfer of carbon from glucose to glutamine may depend on insulin availability.     

Effects of phenotypic plasticity on pathogen transmission in the field in a Lepidoptera-NPV system

In models of insect–pathogen interactions, the transmission parameter (ν) is the term that describes the efficiency with which pathogens are transmitted between hosts. There are two components to the transmission parameter, namely the rate at which the host encounters pathogens (contact rate) and the rate at which contact between host and pathogen results in infection (host susceptibility). Here it is shown that in larvae of Spodoptera exempta (Lepidoptera: Noctuidae), in which rearing density triggers the expression of one of two alternative phenotypes, the high-density morph is associated with an increase in larval activity. This response is likely to result in an increase in the contact rate between hosts and pathogens. Rearing density is also known to affect susceptibility of S. exempta to pathogens, with the high-density morph showing increased resistance to a baculovirus. In order to determine whether density-dependent differences observed in the laboratory might affect transmission in the wild, a field trial was carried out to estimate the transmission parameter for S. exempta and its nuclear polyhedrosis virus (NPV). The transmission parameter was found to be significantly higher among larvae reared in isolation than among those reared in crowds. Models of insect–pathogen interactions, in which the transmission parameter is assumed to be constant, will therefore not fully describe the S. exempta-NPV system. The finding that crowding can influence transmission in this way has major implications for both the long-term population dynamics and the invasion dynamics of insect–pathogen systems. Received: 14 June 1999 / Accepted: 22 March 2000     

A P Element Containing Suppressor of Hairy-Wing Binding Regions Has Novel Properties for Mutagenesis in Drosophila Melanogaster

P elements are widely used as insertional mutagens to tag genes, facilitating molecular cloning and analyses. We modified a P element so that it carried two copies of the suppressor of Hairy-wing [su(Hw)] binding regions isolated from the gypsy transposable element. This transposon was mobilized, and the genetic consequences of its insertion were analyzed. Gene expression can be altered by the su(Hw) protein as a result of blocking the interaction between enhancer/silencer elements and their promoter. These effects can occur over long distances and are general. Therefore, a composite transposon (SUPor-P for suppressor-P element) combines the mutagenic efficacy of the gypsy element with the controllable transposition of P elements. We show that, compared to standard P elements, this composite transposon causes an expanded repertoire of mutations and produces alleles that are suppressed by su(Hw) mutations. The large number of heterochromatic insertions obtained is unusual compared to other insertional mutagenesis procedures, indicating that the SUPor-P transposon may be useful for studying the structural and functional properties of heterochromatin.     

Human baby hair amino acid natural abundance 15N-isotope values are not related to the 15N-isotope values of amino acids in mother’s breast milk protein

Since exclusively breast-suckled infants obtain their nutrient only from their mother’s milk, it might be anticipated that a correlation will exist between the ¹⁵N/¹⁴N isotope ratios of amino acids of protein of young infants and those supplied by their mother. The work presented here aimed to determine whether amino nitrogen transfer from human milk to infant hair protein synthesized within the first month of life conserves the maternal isotopic signature or whether post-ingestion fractionation dominates the nitrogen isotope spectrum. The study was conducted at 1 month post-birth on 100 mother–infant pairs. Isotope ratios ¹⁵N/¹⁴N and ¹³C/¹²C were measured using isotope ratio measurement by Mass Spectrometry (irm-MS) for whole maternal milk, and infant hair and ¹⁵N/¹⁴N ratios were also measured by GC-irm-MS for the N-pivaloyl-O-isopropyl esters of amino acids obtained from the hydrolysis of milk and hair proteins. The δ¹⁵N and δ¹³C (‰) were found to be significantly higher in infant hair than in breast milk (δ¹⁵N, P < 0.001; δ¹³C, P < 0.001). Furthermore, the δ¹⁵N (‰) of individual amino acids in infant hair was also significantly higher than that in maternal milk (P < 0.001). By calculation, the observed shift in isotope ratio was shown not to be accounted for by the amino acid composition of hair and milk proteins, indicating that it is not simply due to differences in the composition in the proteins present. Rather, it would appear that each pool—mother and infant—turns over independently, and that fractionation in infant N-metabolism even in the first month of life dominates over the nutrient N-content.     

Application of a biomarker battery for the evaluation of the sublethal effects of pollutants in the earthworm Eisenia andrei

We applied a battery of biomarkers in the earthworm Eisenia andrei to assess the pollutant-induced stress syndrome. Earthworms were exposed to sublethal concentrations of copper (1-10 microM) and benzo[a]pyrene (0.01-10 microM) as models of inorganic and organic pollutants for 1, 3 and 7 days. Four potential biomarkers of stress were measured: lysosomal membrane stability of coelomocytes, lysosomal accumulation of lipofuscin in chloragogenous tissue and of neutral lipids in coelomatic cells, plasma membrane Ca2+-ATPase activity in the intestinal epithelium; metallothionein content was also evaluated as a biomarker of exposure. Significant changes were observed in the parameters measured in earthworms exposed to both contaminants. Certain biomarkers, such as lysosomal membrane stability and Ca2+-ATPase activity, that showed a decreasing trend with increasing pollutant concentration and time of exposure, proved to be particularly suitable to describe the evolution of a stress syndrome from its early phase to the development of pathological conditions. On the other hand, contaminant-induced changes in lysosomal lipofuscin and neutral lipid accumulation showed a bell-shaped trend, indicating that these biomarkers are able to follow the development of pollutant-induced stress syndrome as far as an equilibrium in the cell functions is maintained; therefore, they are particularly useful to describe mild stress conditions.